This invention relates to an apparatus for the amplification of the intensity of an optically produced image.
One of the first of the devices designated as an optical image amplifier has been disclosed in Swiss Pat. No. 301,222. The fundamental principle of this known device includes a first system of bars placed parallel to and spaced apart from each other. The first bars are reproduced by means of a reflecting surface onto a coordinated second system of bars. The reflecting surface is placed on a control surface capable of deformation by electrostatic field forces, and which together with a photoelectric conductor layer, is located in an electrostatic field. The imge to be amplified is reproduced in a screened form on the photoelectric conductor layer, whereby the electrostatic field is locally altered in keeping with the image, and a corresponding deformation of the control layer, and thus of the mirror image, is effected. The deformed reflected image is reproduced between the bars of the second system of bars onto a projection screen upon which, a brighter image corresponding to the image to be amplified, becomes visible.
To generate the electrostatic field in this first device, two transparent homogeneous electrode surfaces are present. The electrodes are connected with the photoelectric conductor layer and the control layer, respectively, and with an electrical power source. During the illumination in keeping with the image of the photoelectric conductor layer, the electric resistance of the latter varies. By means of the variation of resistance in the longitudinal direction, i.e. parallel to the electrical field, the division of voltage between the photoelectric conductor layer and the intermediate space between it and the control layer is varied locally, whereby a corresponding deformation of the control layer, and consequently of the reflecting surface, is effected.
The utilization of the variation of the resistance of the photoelectric conductor layer in the longitudinal direction has a number of limitations. For example, to obtain a somewhat usual control effect, a relatively large minimum thickness of the photoelectric conductor layer is required, which on the other hand invokes the risk of interfering space charges.
In Swiss Pat. No. 378,432, a second optical image amplifier is disclosed wherein the limitations of the aforementioned known image amplifier are to avoided in that, rather than longitudinal, the transverse local electrical conductivity, or resistance variation of the photoelectric conductor layer, is utilized. The electrode in contact with the photoelectric conductor layer is in the form of a strip grid, wherein the electrically conducting strips located adjacent to and uniformly spaced from each other, extend orthogonally to a first system of bars and are connected in an alternating sequence with one and the other pole of the electrical power source. This electrode grid is preceded on the illumination side by an optical strip grid with the strip preferably extending at an angle of 45.degree. relative to the electrode grid.
With this electrode configuration and layout, the potential distribution in the photoelectric conductor layer varies under illumination and the potential distribution in the layer determines exclusively the forces acting on the control layer and the mirror surface, respectively. The photoelectric conductor layer may therefore be as thin as desired, provided that electrical resistivity is not affected by a by-pass of its support. In addition, the difficulty inherent in the known longitudinal resistivity modulation of a high specific electrical resistivity of the layer is also eliminated, as the appropriate choice of the potential between the electrode strips and the thickness of the layer permits the use of any practically available value.
In spite of these improvements relative to the image amplifier operating with longitudinal modulation, the second image amplifier described above is not widely used due to certain limitations. One of the principal limitations is that with the electrode configuration using alternating polarities, an undesirable base transformation of the control layer appears, which is very much larger than the useful deformation generated by the imaging illumination. This unfavorable relationship between the base and useful deformation is equivalent to a low sensitivity and reduced efficiency of the entire layout.
An apparatus appreciably improved with respect to efficiency and short circuit sensitivity relative to the second system, is a third device disclosed in U.S. Pat. No. 4,519,682. In this apparatus all of the strips of the electrode present in the form of a strip grid, and adjacent to the photoelectric conductor layer, are at the same potential relative to the counter-electrode. The image to be amplified is projected onto the photoelectric conductor layer with the grid extending orthogonally to the bars. Optical screening of the image is effected by a reflecting grid, an absorption grid on the surface of a fiber plate, or by the photoelectric conductor layer consisting of individual strips. Furthermore, the image to be amplified may be projected in a grid form or illuminated in such a manner. The system has a very slight base deformation of the control layer and therefore possesses a relatively high sensitivity and a high efficiency.
The third device has certain limitations, however. For example, the relatively high dielectric constant of a glass support layer located above the electrode grid, causes homogenization of the electrical field, which requires relatively high voltages for a given deformation of a gel layer and a relatively large grid spacing with a given air distance between the two electrodes. Further limitations include space charge effects in the photoelectric conductor layer which lead to the burning in of the image (permanent deformation of the gel layer).
Other image amplifiers are disclosed in Swiss Pat. No. 454,296, U.S. Pat. No. 3,638,027 and U.S. Pat. No. 4,023,969. The image amplifiers known from these other references include limitations similar to those described above.
The foregoing illustrates limitations known to exist in present devices. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one of more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.